1. Field of the Invention
This invention relates to a method of making a magneto-optical recording medium such as magneto-optical disk used for large-capacity data files or the like. This invention particularly relates to a method of forming a magneto-optical recording layer of the magneto-optical recording medium by a sputtering process.
2. Description of the Prior Art
Optical recording media have various advantages such that they can record information at a high density, have a large capacity, and need not be contacted with a head. Among such optical media, the magneto-optical recording medium has attracted particular attention for enabling easy erasing and rerecording.
The magneto-optical recording medium is composed of a magnetic material as a recording medium material, and records information based on changes in magnetization of the magnetic material. For example, an amorphous magnetic material composed of a combination of a rare earth metal such as Gd, Tb or Dy with a transition metal such as Fe, Co or Ni is used as the magnetic material. The magnetic material is used in a layer form as a recording layer.
The recording layer has heretofore been formed by sputtering processes. Among the sputtering processes, a direct current sputtering process is considered to be efficient since the process has the advantages that it is easy to increase the film forming speed and that film formation is possible at low temperatures and it is easy to maintain a magnetic material in the amorphous condition.
However, the direct current sputtering process has the drawback that the molecule density of the recording layer formed by the process is lower than the molecule density of a recording layer formed by the radio-frequency sputtering process, and adhesion of the recording layer to a substrate is also low.
On the other hand, for such reasons that the vertical magnetic anisotropy should be increased, a recording layer may be formed by alternately overlaying the thin layers of a rare earth metal and thin layers of a transition metal. In this case, formation of both the thin rare earth metal layers and the thin transition metal layers by direct current sputtering is advantageous over the formation by radio-frequency sputtering in that the film formation can be achieved at low temperatures and it is easy to increase the film forming speed. However, with the formation by direct current sputtering, the aforesaid problems as well as the problems with regard to deterioration of the squareness ratio and the initial C/N ratio and an increase in deterioration of properties with the passage of time arise.